Water system

[richardwist]

I have a 2007 Holiday Rambler 40’ class A. My water pump functions properly when my tank is full but when the tank gets low the pump runs continuously and only develops a little pressure. I replaced the pump thinking it might be faulty but no change with a brand new pump. I have searched for leaks and cannot find any. The lower the water level in the tank the more the pump runs and the lower the pressure. I have asked a couple of RV techs and all they do is scratch their head and cannot come up with a solution 

[Analyte]

I don't have an answer for you, but I've been looking at a similar situation. No water in my holding tank, and the pump keeps coming on by itself. No leaks found so I pulled the fuse to avoid burning up the pump. No idea why it started doing that.

[Dr4Film]

Has anyone made any major modifications to the water pump system by changing it drastically from when it was first put together at the factory?

I would look closely at the fresh water tank output water line going to the pump, where it is located, also where is the pump located relative to the tank.

Is the pump sucking air once it gets to a lower level?

You need to get into these areas to follow the water lines, etc.

[waterskier_1]

Just thinking out loud here, which may inspire someone to a solution.  The water tank pick-up tube extends almost all the way to the bottom of the tank, typically.  The weight of the water (head pressure) should not be significant to stop the pump.  I'm leaning to thinking there is a problem with the pickup tube in the tank.  If it compromised, like maybe a crack, which would allow air to enter after the water got below a certain level, the pump would start drawing air with the water and cause a similar symptom to that which you describe.  If the "crack" was vertical, starting from the level you notice the pump not working correctly, and extends downward, the lower the water level, the more of the crack exposed, and the more air would be sucked with the water, reducing flow and pressure.  I have never seen the actual construction of the pickup tube so I don't know if this hypothesis could even happen.  I've never even had occasion to look at how the pickup tube is connected to the outside world.  I know some fuel tanks you can remove the pickup tube from the tank.  Is this possible on the water tank?  I know clearance would be a problem.  What I'm thinking is if you could insert a new tube, even temporarily, into the tank and check operation of the water system, that may help isolate the problem.

I can't see how a leak in lines outside the tank would be affected by water level.

  -Rick N. 

[Ivan K]

I don't know if it is a norm but our tank outlet is at its side, as low as they could mount it and the pump is also at the floor of wet bay so it alway has some gravity feed to its inlet. I know that most pumps I worked with are good at pushing but not so much at sucking, especially when a bit worn. Not saying that's the case with the pump in question but if positioned well above the tank level, maybe something to investigate. Or a plugged vent line?

Edited November 10, 2023 by Ivan K

[Dr4Film]

Both our previous Windsor and the Dynasty have the fresh water outlet at the very bottom on the side of the water tank which sits on the floor of the tank bay. The water line travels directly to the water pump that is also mounted on the floor.

The OP needs to post exactly how his fresh water tank and water pump are plumbed together.

[TomV48]

6 hours ago, Analyte said:

I don't have an answer for you, but I've been looking at a similar situation. No water in my holding tank, and the pump keeps coming on by itself. No leaks found so I pulled the fuse to avoid burning up the pump. No idea why it started doing that.

With no water in the tank, can't you just turn the pump off.

34 minutes ago, Dr4Film said:

Both our previous Windsor and the Dynasty have the fresh water outlet at the very bottom on the side of the water tank which sits on the floor of the tank bay. The water line travels directly to the water pump that is also mounted on the floor.

The OP needs to post exactly how his fresh water tank and water pump are plumbed together.

In both of  my travel trailers, with just the basic little SureFlo pump, the pump was inside the coach and the tank below the floor.  Neither had and trouble pumping up from below or self priming.  My coach pump is next to the tank, below the water line until the tank is down to the last 15 or 20 gallons, and it does not even have to self prime and works fone.   You must be sucking air somewhere when the tank becomes less than full.

 

On 11/5/2023 at 2:58 PM, cbr046 said:

 

 

Edited November 11, 2023 by TomV48

[MyronTruex]

Try forcing water into the winterizing or drain hose side of the water pump. I know this is not clear, but some air prior to the pump on mine allowed it to act like some sort of air tank versus having a tube filled with water.

The pump was able to overcome the air bubble as such when the tank was full as the op mentions. 

I leared a lesson in a brake systems I installed many years ago. Getting a small air bubble out of the clear tubes was incredibly difficult. No amount of "bleeding" would force the bubble out. I finally came up with a solution and it was nice to have solid brakes on the airplane I was tryiing to build. 

[Tom Cherry]

Several folks have some good suggestions.  Difficult to really focus and trouble shoot without information.  Maybe some “more information” would help…but generically.

Does the original system have an accumulator tank or canister?  If so, they fail.

Has the prefilter, assuming there is one, in the pump been checked and cleaned.

As to the tank and pickup design…..without pictures or some “inspecting” or a sketch, pretty difficult to make a good call.

IF the pickup tube is mounted on the side or near the bottom, and there is a leak in the line from the fresh tank to the pump, then if you filled up the tank….let it sit…marked the top….precisely…. Of the liquid….then wait a week or so, if it drops, there is a crack or split.  With high head pressure or a hydraulic load, then as you pump, even with a small leak of split or such, then the pressure will drop….as the hydraulic load drop (tank level falls”.  That would explain the symptoms.

Now, if the pick up tube is mid or high, like the diesel fuel tubes in our tanks, a hairline split down the side will “dilute” or inject air.  Figuring this out may get tricky.

SOME ways….

Run a temporary line from the pump inlet to the tank.  Drop it in from the gravity (cap) opening.  Duct tape it to hold it stable.  Use a 5 gallon bucket in the shower and the stop watch on your phone’s clock app.  Time it.  Drain out, using the gravity tank dump, half.  Time again.  Do it near the bottom.  If the pump is consistent….then you have a good pump.  

The next, mad scientist, experiment. Fill the tank.  Use a air compressor with a regulator set really low,  put a valve on the air stream. Attach to the pump inlet.  Then open it and have someone look maybe a flashlight into the gravity opening.  Sort of “judge” how much bubbles and turbulence.  Then drop the tank 1/4.  Repeat.

Eventually, if there is a split in a vertical pickup tube, the. There will be way less, maybe NO air bubbles or turbulence.

[amphi_sc]

On 11/10/2023 at 3:02 PM, Dr4Film said:

Has anyone made any major modifications to the water pump system by changing it drastically from when it was first put together at the factory?

I know in my case the factory had the check valve in the wrong location for the "auto fill" function.  It was possible for the pump to be running when the Aladdin system decided to. open the fill solenoid valve, and with the check valve in the wrong place the pump would suck water out of the tank only to back feed to the fill side and thus return into the tank never building up enough pressure to turn the pump off.  Relocating the check valve between the pump output & fill solenoid input fixed that situation.

[inventor1949]

On 11/10/2023 at 1:48 PM, richardwist said:

I have a 2007 Holiday Rambler 40’ class A. My water pump functions properly when my tank is full but when the tank gets low the pump runs continuously and only develops a little pressure. I replaced the pump thinking it might be faulty but no change with a brand new pump. I have searched for leaks and cannot find any. The lower the water level in the tank the more the pump runs and the lower the pressure. I have asked a couple of RV techs and all they do is scratch their head and cannot come up with a solution 

Nothing wrong with the pump or your water system I had the same problem I even took it out and clean it that dint do the trick ether so the solution is? keep water in the tank period. now lets say you have a pressure regulator from a domestic water supply and the pressure is low for you as is for me the pump if left on it will compensate for the lock if pressure.  

[birdshill123]

When the pemp keeps running could the average be returning to the tank. This can happen if the check valve is faulty. On our Monaco they used a cheap poly valve. If your unit also has an Asco valve and it has a spec of sand on the diaphragm that will cause the same problem. However that does not explain why it does not happen with a full tank. Weird. 

 

[richardwist]

I found a valve on down the line that feeds the pump. I don’t know what it goes to because it disappears behind a panel but it somehow got into an open position. I closed it and that seems to have cured the problem.  Thanks to all who responded. It got me to thinking more and tracing more lines.

[Dr4Film]

Sounds to me like the valve you found may have been a By-Pass valve of some sort.

With a full tank of water there is more head pressure but once the tank level dropped there wasn't as much head pressure and the water was going through the By-Pass valve instead of the pump.

It's always good to put eyes on your specific system to understand how it all works.

When I got our Dynasty home a year ago I was puzzled as to why there was a special connection (aka additional water line) on the Black Tank Back Flush System. Later I discover that I was able to flush the Black Tank even when I wasn't hooked to shore water. Nice feature!